1. Field of the Invention
The present invention relates to a display, and more particularly, to a liquid crystal display panel and a method for fabricating the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for improving adhesion between substrates.
2. Discussion of the Related Art
In general, a liquid crystal display (LCD) has two sheets of glass substrates and a liquid crystal layer sealed between the glass substrates, and a thin film transistor (TFT) is used as a switching device for switching a signal voltage to the liquid crystal layer.
Referring to FIG. 1, an LCD is a non-emission device provided with a lower glass substrate 1 having a TFT as a switching device formed thereon, an upper glass substrate 2 having a color filter formed thereon, and a liquid crystal 3 injected between the glass substrates 1 and 2, thereby obtaining an image by electro-optical characteristics of the liquid crystal 3. Since the LCD consumes a low power consumption and is portable, it draws a great attention as a next generation display which can replace a cathode ray tube (CRT).
More specifically, the lower glass substrate 1 has a TFT array 4, a pixel electrode 4a, and an orientation film 8 formed thereon, while the upper glass substrate 2 has a light shielding layer 5, a color filter layer 6, a common electrode 7, and the orientation film 8. The lower substrate 1 and the upper substrate 2 are bonded by a sealant 9, such as an epoxy resin. A driving circuit 11 on a PCB 10 is connected to the lower glass substrate 1 through a tape carrier package (TCP) 12 for generating and forwarding various control signals and signal voltages required for displaying an image on the LCD panel.
The sealant 9 is used for bonding and fixing the two sheets of glass substrates. In addition, it prevents external moisture from penetrating into the liquid crystal because the liquid crystal easily absorbs water. As a result, resistivity of the liquid crystal is lowered, and impurities may be formed therein when the liquid crystal is exposed to the air.
There are an inorganic sealant and an organic sealant. Although the inorganic sealant is used in the early generation LCD, the inorganic sealant is not used any longer as a liquid crystal material is developed. Among the organic sealants, there are epoxy group resins, phenol group resins, and acryl group resins, which may be sorted into two liquid types in which a main agent and a hardening agent are to be mixed in use, and one liquid type containing the main agent and the hardening agent as a single solution.
Depending on methods of hardening in the sealant, there are a thermo-hardening type, and a UV hardening type. Both types are required a strong adhesion, a high crystallinity, a good printability, and the like. Further, for accurately controlling a cell gap, a uniform spreading is necessary when the substrate is under pressing, heating, and curing processes.
The thermo-hardening resin, such as epoxy or phenol, has advantages of a high mechanical strength, a strong adhesion, and a good cross-linking. On the other hand, the UV hardening resin may be a better type in applying a larger sized device because it has a low hardening temperature, and a short hardening time period. Therefore, a thermal expansion problem may be avoided and bonding between the substrates is improved in applying to a large sized substrate.
A related art LCD panel will be explained with reference to the attached drawings. FIG. 2 illustrates a plane view of a related art LCD panel, wherein a first substrate 21 and a second substrate 21a are arranged to face into each other, and a liquid crystal layer (not shown) is formed between the first and second substrates 21 and 21a. Each of the first and second substrates 21 and 21a has an active region ‘A’ and a pad region ‘P’ defined thereon. The first substrate 21 has a plurality of thin film transistors and pixel electrodes on the active region ‘A’ and a plurality of gate pads 23 and data pads 25 on the pad region ‘P’. There is a UV hardening sealant 27 in the pad region ‘P’ on the outside of the active region ‘A’, more specifically, on a pad link part PL, for bonding the first and second substrates 21 and 21a. 
FIG. 3 illustrates a detailed view of an ‘X’ part of FIG. 2, wherein there are a plurality of gate lines G1, G2, . . . , Gn and data lines D1, D2, . . . , Dn formed in the active region ‘A’ on the first substrate 21. The gate lines and the data lines cross one another, thereby defining a plurality of pixel regions each having a pixel electrode 31. There are a TFT (not shown) arranged at each crossing part of the gate lines G1, G2, . . . , Gn and the data lines D1, D2, . . . , Dn.
There are gate pads GP1, GP2, . . . , GPn and data pads DP1, DP2, . . . , DPn, connected to a driving IC, for linking driving signals and data signals applied to the gate pads GP1, GP2, . . . , GPn and the data pads DP1, DP2, . . . , DPn to the gate lines G1, G2, . . . , Gn and data lines D1, D2, . . . , Dn at the active region ‘A’ through gate pad links PL_g, and data pad link PL_d, respectively.
Actually, the gate pads GP1, GP2, . . . , GPn and the data pads DP1, DP2, . . . , DPn are electrically connected to the TCP and anisotropic conductive film (ACF) by a transparent conductive film 33, for receiving the driving signals and the data signals from the external driving IC. The gate pads and the data pads are connected to the TCP and the ACF via the transparent conductive film 33 having a good electrical conductivity and good adhesion because the gate pads and the data pads formed of non-transparent metal have poor adhesion to the TCP and the ACF.
The aforementioned related art LCD panel will be explained in more detail. FIG. 4 illustrates a cross-sectional view along line IV—IV, showing the gate pads of the LCD panel.
Referring to FIG. 4, there are the gate line G1, the gate pad GP1, and the gate pad link PL_g formed on the first substrate 21 having the active region ‘A’ and the pad region ‘P’ defined thereon. The pad region ‘P’ has a region for the gate pad GP1 and a region for the gate pad link PL_g. A gate insulating film 41 is formed on the entire surface of the first substrate 21 including the gate pad GP1. There are a protection film 43 on the gate insulating film 41 and a transparent conductive film 33 passed through the gate insulating film 41 and the protection film 43, and electrically connected to the gate pad GP1.
The gate line G1, the gate pad link PL_g, and the gate pad GP1 are formed as a unit, formed of a non-transparent metal, such as aluminum (Al), chromium (Cr), molybdenum (Mo), copper (Cu), an aluminum alloy, a bilayer of the foregoing metals, or the like.
On the second substrate 21a at the active region ‘A’, there are a light shielding layer 45 extended to a region for the gate pad link PL_g, a color filter layer 47 for displaying colors, and a common electrode 49 and the pixel electrodes 31 (shown in FIG. 3) for applying a voltage to the liquid crystal LC. The photo-hardening sealant 27 along the outside of the active region ‘A’ having the gate pad link PL_g formed thereon, for bonding the first substrate 21 and the second substrate 21a. 
In the meantime, there are thin film transistors and pixel electrodes (both not shown) on the first substrate 21 at the active region. That is, at a portion where the gate line and the data line are crossed, there are a thin film transistor having a gate electrode, a gate insulating film 41 on the gate electrode, a semiconductor layer and an ohmic contact layer on the gate insulating film 41, and a source and a drain electrodes, and a pixel electrode 31 connected to the drain electrode through the protection film 43.
FIG. 5 illustrates a cross-sectional view along line V—V of FIG. 3, in which reference symbol “DP1” denotes a data pad, “D1” denotes a data line, and “PL_d” denotes a data pad link. A detailed description of FIG. 5 will be omitted because FIG. 5 is similar to FIG. 4 except for that the data pad DP1 and the data line D1 are formed on the gate insulating film 41.
Thus, the foregoing LCD panel displays a picture as the thin film transistor is turned on/off in response to the gate signals and the data signals applied from the external driving IC to the gate lines G1, G2, . . . , Gn and the data lines D1, D2, . . . , Dn at the active region ‘A’ through the gate pads GP1, GP2, . . . , GPn and the data pads DP1, DP2, . . . , DPn.
However, the foregoing related art LCD panel has the following problems.
The plurality of pad links are formed of a non-transparent metal in the above-described LCD panel. Thus, when a photo-hardening sealant is applied for bonding the first substrate and the second substrate, a light shielding layer is extended to a portion of the pad link on the second substrate, so that UV light for curing the sealant is blocked by the portion. As a result, bonding of the two substrates becomes defective, and a product reliability becomes poor.
Because of the small margin of the light shielding layer and the pads, the photo-hardening sealant is used to product models for monitors only. The photo-hardening sealant should be applied to the circumference of the optical shield layer because the pads are formed of non-transparent metal. The photo-hardening sealant may be applied to large sized product monitors only. In the case of fabricating monitors, since the light shielding layer is exposed to a region for which the photo-hardening sealant is to be coated, light is directed to a color filter substrate, thereby curing the sealant. However, in the case of the notebook PC, there is no room for opening in the light shielding layer due to a small margin.